1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a resource allocation method and system for removing cell interference between neighbor cells in a communication system having a multi-cell structure.
2. Description of the Related Art
In the next generation communication system, active research is being conducted to provide high-speed services having various Qualities of Service (QoS) to users. Particularly, in the next generation communication system, a study is being conducted to support high-speed services that can guarantee mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a Wireless Local Area Network (WLAN) system and a Wireless Metropolitan Area Network (WMAN) system. An Institute of Electrical and Electronics Engineers (IEEE) 802.16a/d communication system and an IEEE 802.16e communication system are typical BWA communication systems.
IEEE 802.16a/d communication systems and IEEE 802.16e communication systems, which are BWA communication systems, are communication systems employing Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to support a broadband transmission network for physical channels of the WMAN system. An IEEE 802.16a/d communication system currently considers only the state where a Subscriber Station (SS) is fixed, i.e. the state where mobility of the SS is never considered, and the single-cell structure. Unlike IEEE 802.16a/d communication systems, an IEEE 802.16e communication system considers mobility of a SS in the IEEE 802.16a communication system, and an SS having mobility will herein be referred to as a Mobile Station (MS).
In a BWA communication system, because limited resources, i.e. frequency resources, code resources, and time slot resources, are shared by a plurality of cells constituting the communication system, interference may occur between the plurality of cells, especially between neighbor cells. Interference between neighbor cells is considerable in a communication system using a frequency reuse factor of one. More specifically, the use of the frequency reuse factor of 1 can facilitate efficient utilization of frequency resources, but an MS located in a cell boundary between neighbor cells suffers a considerable decrease in a Carrier-to-Interference and Noise Ratio (CINR) of a signal received from a serving Base Station (BS) that manages the cell where the MS is located. That is, in a communication system using a frequency reuse factor of one, an MS located in the vicinity of the serving BS may have no difficulty in communicating with the serving BS due to low interference, but an MS located in a cell boundary suffers interference from a neighbor BS that manages a neighbor cell, thereby decreasing system performance.
In order to remove interference between neighbor cells, the MS improves a received CINR from a serving BS using an interference remover in a downlink interval, and the serving BS improves a received CINR from the MS using an interference remover in an uplink interval, thereby improving system performance. However, a scheme of improving system performance using an interference remover can hardly expect remarkable improvement of system performance, because the interference remover may not accurately remove interference signals or may not correctly restore signals received from the serving BS. With reference to FIG. 1, a description will now be made of a communication system having a multi-cell structure.
FIG. 1 shows a general BWA communication system according to the prior art. Referring to FIG. 1, the BWA communication system has a multi-cell structure, i.e. has a cell1 110 and a cell2 120, and includes a BS1 111 and a BS2 121 that manage the cells 110 and 120, respectively, and an MS 113 that is located in the cell1 110 and receives a communication service from the BS1 111. For convenience, signal exchanges between the BSs 111 and 121 and the MS 113 are assumed to be performed through a first channel h1 and a second channel h2, respectively, using OFDM/OFDMA.
The MS 113 is located in the boundary of the cell1 110, and the BS1 111 transmits data to the MS 113 located in the cell1 110 through a frequency region (A-1) 151. The BS2 121 that manages the cell2 120, which is a neighbor cell of the MS 113, transmits data to MSs located in the cell2 120 through a frequency region (B-1) 161 and a frequency region (B-2) 163. In this case, the MS 113 located in the boundary of the cell 1 110 can receive interference caused by data transmitted by the BS2 121, which is a neighbor BS, while receiving data from the BS1 111, which is the serving BS, through the frequency region (A-1) 151.
In other words, there is an overlapping region where the frequency region (A-1) 151 allocated to the MS 113 by the BS1 111 and the frequency region (B-1) 161 and the frequency region (B-2) 163 allocated to the MSs located in the cell2 120 by the BS2 121 overlap each other. The overlapping region is an interference region for the MS 113 located in the boundary of the cell1 110. Because of the presence of the interference region, if the BS2 121 of the cell2 120 transmits data through the frequency region (B-1) 161 and the frequency region (B-2) 163 using the same time-frequency resources as those of the BS1 111 while the MS 113 is receiving data from the BS1 111 through the frequency region (A-1) 151, the MS 113 located in the boundary of the cell1 110 decreases in the received CINR, causing a decrease in reception performance of the MS 113.
In order to prevent a decrease in the CINR due to interference of the cell2 120, the MS 113 removes interference using the interference remover as described above. However, because the BS1 111 and the BS2 121 allocate resources independently of each other, the interference remover may not accurately remove interference signals or may not correctly restore the signals received from the serving BS1 111. Therefore, it is hard to expect noticeable improvement of system performance.
More specifically, if the BS2 121 of the cell2 120 transmits data through the frequency region (B-1) 161 and the frequency region (B-2) 163 while the MS 113 is receiving data from the BS1 111, or a serving BS, through the frequency region (A-1) 151, the data transmitted by the BS2 121 serves as interference to the MS 113. In order to remove interference, the MS 113 should have information on the overlapping region between the frequency region (A-1) 151, and the frequency region (B-1) 161 and the frequency region (B-2) 163, i.e. information on the interference region. In addition, the MS 113 should have information on a Modulation and Coding Scheme (MCS) level of the data transmitted through the frequency region (B-1) 161 and an MCS level of the data transmitted through the frequency region (B-2) 163, and should also have information on the channel h2 of the cell2 120.
That is, in order to remove inter-cell interference of the cell2 120, the MS 113 should estimate the channel of the cell2 120 using a pilot received from the BS2 121. The need for the information by the MS 113 for the inter-cell interference removal acts as a heavy load to the MS 113, decreasing the system performance. When the MS 113 has a plurality of neighbor cells, the decrease in the system performance can be more considerable.